Wave signaling system



March 17, 1,936. E, F- CARTER 2,034,226

WAVE S IGNALING SYSTEM Filed Sept. l1, 1930l ATTORNEYS lPatented Mar. 17, 1936 UNITED. STATESv PATENT vOFFICE WAVE SIGNALING SYSTEM Emmett Finley Carter, Flushing, N. Y., assignor to United Research Corporation, a. corporation of Delaware Application September 11, 1930, Serial No. 481,104 16 Claims. (Cl. 179-171) trolling the signal response at the low-frequency end of the audio-frequency band in order for example, to improve the fidelity of sound reproduction.

A further object is'to provide an arrangement for variably adjusting the degree of amplification with respect to frequency in order to peak the frequency-response curve at a desired point Awithin the audio-frequency band with the view of adjustably controlling the emphasis. Y

With respect to the` first object mentioned, there exists in manyv types of low-frequency region of tonal thermionic amplifiers, especially those embodied --in modern radio broadcastv receivers, several principal causes for a disproportionate reduction in amplification `.at the low audio-frequencies. One of these causes resides inthe high impedance at such frequencies of the blocking or coupling -condensers frequently associated with the voutput circuits'of the low-frequency amplifier stages for separating the alternating and ,direct-current components. -The coupling condenser although of capacity sufficiently large to introduce negligible loss throughout the major portion of the .audible range, produces appreciable attenuation asthe low-frequency limit is approached -due to the marked increase in its impedance. Another principal cause for a disproportionate reduction of the lower audio frequencies is due to negative regeneration causedvby insufficient by-passing of the low-frequency currentsby the condens-er in shunt to the grid biasing resistor usually interposed in the anode circuit of a thermionic element for applying a suitable' ne'gative biasing potential to the grid thereof. A third cause may result from insufficient inductance in one orfmore of the vinte'rstage audio-frequency transformers at the very low frequencies' due to an economical design.

templated to compensate in greater or less de- `gree as desired, for any orall of the above effects In accordance with this invention it is conimpedance associated with the anode circuit of an amplier stage. In this way a regenerative action is obtained which varies automatically with frequency in opposite fashion to that of the attenuation effects noted andthus is admir- 5 ably adapted to compensate for such effects.

The principle of this invention is susceptible of embodiment in many specific forms several of which are included herein by way of illustration. In one embodiment the regenerative'cir- 10 cuit is constituted by arranging a blocking condenser in the grounded cathode lead extending to the output circuit of an amplifier stage in'- stead of inthe anode lead, the latter being the usual connection. The regenerative circuit is 15 then constituted by coupling the ungrounded terminal of the condenser to a control electrode of a preceding detector or audio-frequency amplifier stages which is so coupled to the tube containing the condenser as to accomplish a re- 20 versal phase of the signal Wave. As a consequence of this arrangement energy is fed back to the preceding tube in like phase relation with the incoming signal which tends to accentuate the lower audio-frequencies.

If desired the regeneration due to the blocking condenser or other mentioned vcapacitive impedance may be adjustedto normally increase the low-frequency response to a point where it' exceeds that of the higher frequencies. The 30 gridv biasing impedance of the detector or an amplifier stage may then be rendered adjustable: to vary the degree of low frequency negative regeneration thereby providing .a means of varying the low-frequency response with respect to 35.'

the higher frequencies. In this manner the peak of the frequencyresponsel characteristie may be shifted throughout the frequency range for adjusting the region of tonal emphasis to a desired frequency without the necessity 40 thermionic tube V1 of the screen-grid type arthe above noted ranged to operateas a 4contains a low frequency T the secondary winding to the actuating coil of a dynamic type.

A blocking condenser C prevents the flow' of direct current through the primary winding of transformer T, and accordingly. the space current for tube V'.- supplied from battery' F is returned through the field winding of the loud speaker unit. The blocking condenser Co wo'uld normally be included at X in the anode lead -of the transformer primary Winding,

but in the present instance is included in the cathode lead thereof as shown inorder to accomplish the ends of the present invention.

The filaments of tubes V1 and Vz may be heated 'in any suitable manner. (not shown) the cathodes -in each instance being connected to ground through grid biasing resistors R1 and Rz shunted by the low-frequency by-passing condensers C1 and C2 respectively, for applyingsuitable negative biasing potentials to the respective gridsv inI accordance with the space supply currents ilowing through the resistor elements. This method of biasing the grids of the 'tubes while convenient and in many respects advantageous, is subject to the objection that it operates degeneratively upon the signaling current.

Thus referring more* specifically to tube V1, assume that at a given instant a signaling wave impressed upon the input thereto is s uch as to increase the negative potential of the grid electrode relative tov the cathode. In accordance with the .well-known operation of the tube, there will result a corresponding momentary decrease in the flow of spacercurrent which correspondingly reduces thepotential drop across the resistor R1 and thusin turn reduces the resultant negative potential applied to the grid of thel tube, inthis manner offsetting in some degree the effect of the applied signaling wave with.

consequent reduction in amplitude of the output current. In order to minimize this effect the by-passing condenser C1 is connected in shunt tothe resistor element R1, thereby affording a low impedance path around theresistor which reduces degenerativeaction -to a negligible degree throughout the major portion of the audio-frequency band. Atl the lower audiofrequencies, however, they impedance of the bypassing condenser C1 increases to such an extent as to introduce marked degenerative'action with consequent reductionin amplification.'

It will be observed that .theA attenuation' due to the degenerativeaction ofl the grid biasing impedance R1-C1 produces the same -kind of distorting effect upon they fidelity of signalreproduction as does the blocking 'condenser Co. Hence the distortion'due. to 'either or both of these sourcesmay be compensated by regeneratively applying a portion of 'the voltage drop due to the signal wave which exists across the` condenser Co to a control electrode of tube V1.

The regenerative coupling is inthe present instance accomplished by connecting the ungrounded terminal ,of condenser Co` through a second blocking condenser C3 and afreslstance Rato a control electrode, specifically the screen grid electrode of tube V1. The screen -gridl of' tube V1 is in turn connected through a resistance R4- to a point of suitable biasingpotential-on battery F; whereas a condenser@l adapted to by-pass ,the radio and is connected from the the ungrounded terminal lSIStOr R1. l

The regenerative scre'en grid electrode to action with the coupling conaccomplished between tubes V1 and Va as a re-j sult of-the well understood action of the resistance coupling circuit E. If a transformer were used in place -of circuit E,the same result could' be attained by Properly poling the secondary relative to the primary'winding.

The amount of feed-back maybe controlled bythe relative proportioning of resistances Ra and R1 thereby controlling the potential applied p to' the screen grid electrode. The upper frequency limit 'at which it is desired that the regenerative action become effective is controlled higher audio frequencies,

of the grid biasing re v nection shown results fronr the reversal in phase by properly proportioning the capacities Co and C4; while the frequency below which it is d esiredthat the regenerative action cease is deter.-` mined by the magnitude of capacity Cs.

The regenerative action may, if desired', be adjusted to counterbalance exactly the decrease I in amplification otherwise present at the lower frequencies, vin which eventi the frequencyre' spense characteristic of the amplifier will be substantially constant down to the low frequency-1 cutoff point. AOn the other hand it is perfectly feasible with the arrangement described to either over emphasize or under emphasize the low frequencies throughout a desired portion 'ofthe' audio frequency spectrum. This suggests the po trolling the frequency response characteristic in the manner described td peak the characteristic l vat any desired frequency thereby adjustably controlling the region of tonal emphasis, as is sometimes desired in radio reception for bringing out more distinctly the low, intermediate or high frequency notes as the case may be.

A circuit vfor accomplishing this end which operates Very efficiently in "conjunction with the regenerative circuit described comprises the vari- .able resistance R5 C5 bridged across the resistor Rr upon closureA of switch K. The capacity C5 is made suiliciently` large I'that with resistance'R5 adjusted to zero it will in conjunction with capacity C1 satisfactorily by-pass `around resistor R1 the entire range of'v audio-frequency currents. As resistance R5 is increased in magnitude, however the degenerative action described above will be ever increasing prominence and will extend over an increasing portion of the audio frequency band beginning with the low frequency end.

in series with avxed capacity l introdued, withl sibility of variably conlio denserlCo is soproportioned as to greatly over'- 1 V emphasize or accentuate the lowerv frequencies with resistance R5 at zero, it will be apparent that steadily increasing the' magnitude of -this resistance will cause the peak value ofampliflcation to shiftfrom-the low frequency end of the audic- 60. If nowthe regenerative circuit including con- Curve b shows the result obtained with the re- 4sistance R5 adjusted to such value as to obtain substantially uniform response over the essential range of audio frequencies; whereas curve c shows an adjustment of R5 to a high resistance value such as to over emphasize the upper limit of the audio-frequency band.`

The invention disclosed herein is susceptible of specific embodiment in a number of different ways. For example, in the circuit arrangement of Fig. 3 the regenerative action is obtained by connecting a pair of resistance elements Re and R7 in series between the anode of tube V2 and ground. A point between the resistance elements is connected directly to the screen grid of tube V1 and also through a condenser C1;` to ground. The

circuit of ltube V2 impresses a potential drop across resistance elements Re and R1 a portion of which is applied to the screen grid electrode of tube V1 and thereby may be proportioned to accentuate the lower audio-frequencies to the extent desired. p 'I'he relative magnitude of' resistances Re and R1 are determined by the portion of the potive potential of battery F to be applied as a biasing potential to the screen-gridelectrode of tubes V1. The actual magnitude of elements Rs and R7 is determined on the basis of the signal current potential to be applied to the screen-grid of tube V1 'in order to accomplish the desired degree of regeneration. The point in the frequency scale 40 at which the regenerative action commences as well as the rate of increase of the regenerative effect toward the low frequency limit is determined f by the value of capacity Cewith reference to that of resistance Re.

It will be noted that the impedance Cs-(Rs While capacitively reactive and hence of increasing impedance to decreasing frequencies for accentuating the lower audio-frequencies, 'is nevertheless definitely limited in ultimate magnitude to that of resistance Re. This definite limitation in maximum value of impedance Cs-R-e prevents the regenerative effect from becoming excessive at the very low audio or sub-audio-frequencies to render the amplifier unstable by causing it to o flutter or motorboat as the condition is termed. Inasmuch as elements Re and R1 are vbridged in series across the primary winding of transformer T the impedance of which decreases with frequencies, this factor also becomes effective to limit the regenerative action at the sub-audiofrequencies for preventing yunstable operation of the circuit. f

Itv is apparent of course that the' capacitive impedance C11- Rs of Fig. 3, serves the same purpose insofar as the regenerative efect is conc'erned as the blocking condenser C0 of Fig. 1 and is thus an alternative scheme for accomplishing the objects of the invention. b i

It is not necessary that the regenerative potential be applied to the screen-grid electrode of tube V1 as is shown in the modification of Figs. 1 and 3, the action being equally well obtained by coupling the regenerating voltage drop across the capacitive impedance element back to the grid circuit of the preceding tube V1 as is shown, for example,

amplified signaling current flowing in the output I vin Fig. 4. In 4 the ungrounded terminal of the' blocking condenser Co of Fig. 1 is connected through capacity C3 and resistance R3 to the ungrounded terminal of a resistance R8 shunted by a capacity Ca interposed in the ground lead extending from the grid electrode of tube V1. The

energy fed back from capacity C11 flows through resistor Ra in additive phase relation to the incoming signal impressed upon terminals I, and.-

thus serves to offset the degenerative action caused by the flow of current in the grid biasing impedance Rif-C1 connected to thecathode of tube V1.

It will be observed that the arrangement ofl Fig. 4V is well adapted for use in conjunction with triode tubes. It will be observed further with specific reference to Fig. 4 that the tube V1 need not necessarily be a detector tube-having a tunable input circuit associated therewith, but may vwith equal facility comprise a stage of audiofrequency amplification connected to input ter'- minals I through a suitable resistance coupling circuit H or other untuned low frequency network.

'I'he regenerative circuit of Fig. 3 may of course by obvious changes extend to the grid circuit of tube V1, after the fashion shown in Fig. 4.

What is claimed is:

1. In a wave signaling system, a plurality of space discharge elements coupled in tandem, one of said elements having a control electrode, and a succeeding element having an anode and a cathode, the anode-cathode circuit of said succeeding element including a blocking condenser connected between the cathode and theoutput circuit thereof, and a lead containing a condenser connected between the terminal of said blocking condenser remote from said cathode to said control electrode.

2. In a 4wave signaling system, in combination,`

al first thermionic space discharge element coupled vin tandem to a second space discharge element, each said element having anode, cathode and controll electrodes, a source of anode potential for said elements, an output coupling means for said second element, a blocking condenser in series with said output coupling means for preventingA the passage of direct current ,through said output coupling means, and a regenerative vpath from said blocking condenser to a control electrode of said first element for compensating low frequency discrimination of said blocking condenser.

3. A combination according to claim 2 in which said regenerative pathcompr-ises a condenser and .a resistance in series.

, 4.v In a wave 'signaling system, vin combination a first thermionic space discharge element cou pled in tandem to a second space discharge element, said elements having anode, cathode and control' electrodes, a source of anode potential for said elements an output coupling means for said second element, a blocking condenser in series with said output coupling means for preventing the passage of direct current through said output coupling means, la regenerating path kfrom said blocking condenser to a control electrode of said first element, a resistance in said regenerating path and a resistance in said control circuit. the

values of which resistances control the degree of regeneration.

5. In'combination, a thermionic detector having an anode, a cathode, a screen-grid for screening the detector anode and an input grid, a thercondenser in series,

mionic amplifier having an anode. cathode and grid, a source of anode potential for said amplifier and detector, the anode circuit of said detector being coupled to amplifier through signal wave phase reversing means, an output circuit for said amplifier, comprising an output transformer and a blocking the first terminal `of said condenser being lconnected to said ampliner cathode, and a'regenerat'ive feed-back connection from the second terminal of said condenser to the screen-grid of said detector, whereby tonal I distortion occasioned by said blocking condenser system, a pair of space control electrodes, means for supplying anode potential to said anodes, a

is compensated. 6. In a `low frequency electric wave signaling discharge devices having cathode, anode and resistor in the anode circuit of the first of said devices for furnishing negative biasing `potential to the grid thereof, a low frequency by-passing condenser shunted across said grid4 biasing resistor, a capacitive impedance in the anode circuit of the'second of said space discharge ldevices, anda regenerative wave path leading from said capacitive impedance to a control electrode cade connection, each pacitive impedance cuit of one said tube, and a grid biasing imsound reproducing system,

`onic tubes in cascade connection,

of said first device whereby tone distortion due to said capacitive impedance and resistor circuit may be compensated.

7. In a low frequency and sound reproducing electric wave signaling system, a pair of thermionic space discharge devices arranged in casdevice having anode, cathode, and control electrodes, a capacitive' impedance associated ond of said devices having one terminal connected to the cathode thereof, a regenerative path extending from the other terminal thereof to a control electrode of the first of said tubes proportioned to accentuate the lower audio-frequencies, f of said first de- 'l and a mesh in the anode circuit vice, said mesh comprising a grid-biasing resistance, capacity and variable resistance for adiusting the tonal emphasis of reproduced sound.

8. In an audio-frequency wave signaling and each tube havinganode, cathode and control, electrodes, a caincluded in the anode cirpedance including resistance shunted by. capacity arranged in the anode circuit of a preceding tube, means forl regeneratively applying upon a controlv electrode of said preceding tube a po` the signal wave voltagek capacitive vimpedance tential dependent'upon which exists across said and proportioned to .increasingly accentuate the frequencies toward the low frequency end of audible frequency range, and means .comprising a fixed capacity in shunting said grid biasing impedance. for adjustably controlling the degree of said regeneraobsessethe grid circuit of said with the output circuit ofthe seca plurality of thermi series with variable resistance thermionic tub'es in cascade connection, each tube having anode, cathode and control electrodes, resistance connected from the anode of one said tube to a point of ground potential, a 'regenerative connection from an intermediate tap of said resistance to a control electrode of one said tube, and a ycondenser connected from said control electrode to ground, the degree of saidv regeneration being dependent upon the relative magnitude of the tapped resistance portions, said capacity increasingly controlling said regeneration toward the lower audio-frequencies. v

11. In a low frequency wave signaling system including a pair of thermionic tubes in cascade connection, each tube having anode, cathode and control electrodes, resistance connecting the' anode of the second said tube to a point of ground potential, a regenerative connection from an intermediate tap of said resistance to a control electrode of the first said tube, and a condenser connecting said control electrode to ground, the vtapping point on said resistance and the magnitude of said capacity being selected to increasingly. accentuate the lower audio-frequencies and means for adjustably controlling the region of tonal emphasis of said system comprising a4 ,grid biasing resistor shunted by. capacity included in the anode circuit of said rst tube, and y capacity and variable resistance in' series shunting said resistor.

12. -A signaling system comprising a plurality of vacuum tubes in cascade connection, each tube having anode, cathode and grid electrodes, a coupling condenser in circuit between said tubes, and an audio frequency selective circuit from the output circuit of a succeeding tube to -the input circuit of a preceding tube of said cascade,` a .condenser in the output circuit of said succeeding tube and a direct lead from said condenser to a grid of a preceding tube.

13. The combination of aline adapted to transmit a band of audio frequency currents, a vacuum tube amplifier therefor, and means lcomprising an adjustable device in circuit with said a'mpliiler whereby said adjustable device in successive positiornsv of its adjustment is adapted respectively to (a) peak thefrequency response of said band oflcurrentsas frequencies less than 350 cycles per second, (b) uniformly transmit said band of currents over a wide rangeof frequencies and v(c) peak the frequency response of said band of currents in the high frequency portion of said band above 350 cycles per second. j

`14. Arrangement for transmitting a band of audio frequency currents inmodified wave form comprising the combination of a line adapted to transmit a band of audio frequency currents, a vacuum tube amplifier therefor, and adjustable means-in circuit with saidampliiler adapted to (a) `peak the frequency response ofI said band of currents in the low frequency portion of said.

band, (b) uniformly transmitsaid .band of currents over a wide range of frequencies, and (c)` peak the frequency-response of said band of cur- A rents in the high' frequency portion of said band. 1 5. Arrangement for transmitting a band of audio frequency currents in modified wave form comprising the combination of a line adapted to transmita Aband of audio frequency currents. a vacuum tube amplifler therefor, adjustable means in circuit with said amplifier adaptedk to (a) peak the frequency response ,of said band of currents in the low'frequency portion of said band,

-(b) uniformly transmitl said' band of currents over awide range of frequencies and (c) peak the frequency response of said band of currents in the high frequency portion of said band, and means for limiting the frequency range within which said adjustable means is effective.

16. Arrangement for transmitting a band of audio frequency currents in modified wave form comprising the combination of a source of a band of audio frequency currents, a vacuum tube 10 amplifier therefor, and adjustable means in circuit with said amplier adapted to peak the frequency response of said band of currents at selected portions of said band from. the low frequency portion ofl said band to the high frequency portion thereof, and to gradually shift the peak over a Wide range of frequencies, and at another point of adjustment to uniformly transmit saidband of currents over a wide range of frequencies.

EMME'IT FINLEY CAR'I'ER. m 

